1. Field of the Invention
The invention relates to a radiation-sensitive mixture which contains a polymeric binder having acid-labile side groups and a compound which generates a strong acid on irradiation.
In addition, the invention relates to .alpha.,.beta.-unsaturated carboxamides with which the polymers used as binders can be prepared and to the polymers so prepared.
2. Description of the Related Art
A frequently used positive-working radiation-sensitive mixture for producing radiation-sensitive recording materials contains an o-quinonediazide derivative and a binder which is soluble in aqueous-alkaline solvents, for example a novolak or a polyhydroxystyrene binder. However, the sensitivity of these systems to radiation, in particular shortwave radiation, is sometimes unsatisfactory. Due to their high intrinsic absorption, novolaks are unsuitable as binders in an insert resist material for deep UV lithography (220-330 nm). By contrast, polyhydroxystyrenes have more favorable absorption properties and are additionally distinguished by a better heat holdout. However, polymers of this type are accessible only by involved multi-stage syntheses. The lithographic properties of polymers composed of unsubstituted hydroxystyrene are unsatisfactory because of their unbalanced hydrophilic/hydrophobic character both in 3-component systems and in 2-component systems. There is therefore a need for binders for highly resolving, highly sensitive resist materials which have good transparency even in the UV-2 region and a high heat holdout, and which can be developed under aqueous-alkaline conditions.
Mixtures which exploit the principle of the so-called "chemical intensification" i.e. which contain, in addition to an acid-cleavable compound, a compound which releases a catalytically acting acid under the action of radiation, generally show a higher radiation sensitivity. Examples of the acid-generating compounds are diazonium, phosphonium, sulfonium and iodonium salts, nitrobenzyl esters, phenolic methanesulfonates, diazo compounds and halogen compounds. The use of onium salts as photochemical acid generators in resist materials is known, for example, from U.S. Pat. No. 4,491,628. A review of the use of onium salts in resist materials is given by Crivello in Org. Coatings and Appl. Polym. Sci., 48, pages 65-69 (1985).
Radiation-sensitive mixtures of polymers with acid-labile side groups and photochemical acid generators are known from U.S. Pat. No. 4,491,628 and FR-A 2,570,844. However, only polymers of para-substituted styrene or .alpha.-alkylstyrene are completely disclosed in these two publications. Only tert.-butoxycarbonyloxy groups and trialkylsilanyloxy groups are listed as acid-labile para-substituents. The polymeric binders with the acid-labile side groups are extremely hydrophohic. The acid generated on exposure effects elimination of the acid-labile protective groups and thus causes the polymeric binders to become soluble in alkali.
Copolymers having acid-labile groups bound via a phenolic oxygen atom, for example copolymers of p-hydroxystyrene and p-(tert.-butoxycarbonyloxy)styrene, are known from J. Poly. Sci., Part A, Polym. Chem. Ed., 24:2971-2980 (1986).
The polymers described in German Patent Application P 4,120,172.8 show a marked improvement of the transparency properties in the desired wavelength region. It is achieved, however, only by introducing a high proportion of acid-labile protective groups, whereby the hydrophobic/hydrophilic balance is, adversely affected. Moreover, there are as a rule adhesion problems in systems which contain highly hydrophobic binders.